Flooding is the most damaging natural disaster worldwide, andthe flood-vulnerable population is expected to grow in comingdecades (1). Flood risks will likely increase because of bothclimate change (1) and shifting land uses, such as filling ofwetlands and expansion of impervious surfaces, that lead tomore rapid precipitation runoff into rivers. …

Flood-control infrastructure (e.g., levees) prevents high flowsfrom entering floodplains, thus diminishing both natural floodstoragecapacity and the processes that sustain healthy riverside forestsand wetlands. As a result, floodplains are among the planet’smost threatened ecosystems, even though functioning floodplains—thoseconnected to rivers—are among the most valuable ecosystemsfor supporting biodiversity and providing goods and servicesto society (6, 7). We propose that a large-scale shift in landuse and policy is urgently needed to achieve economically andenvironmentally sustainable floodplain management. The areaof floodplains allowed to perform the natural function of storingand conveying floodwaters must be expanded by strategicallyremoving levees or setting them back from the river.

Floodplain reconnection will accomplish three primary objectives:flood-risk reduction, an increase in floodplain goods and services,and resiliency to potential climate-change impacts. Effortsshould focus on strategic reconnection of large areas of floodplaincurrently used for agriculture, as large-scale reconnectionof densely populated floodplains would be considerably moreexpensive. The changes we propose will confront considerablesocioeconomic and political challenges, but we believe thesecan be overcome by promoting floodplain land uses that are consistentwith private ownership and a vibrant agricultural economy. Althoughour specific recommendations are for the United States, thisvision is applicable worldwide. Similar calls for change havebeen made in several countries [e.g., (8)].

Reduced Risk, Enhanced Benefit

Large-scale floodplain reconnection will reduce flood risk intwo ways. First, land use within reconnected floodplains willmove toward activities compatible with periodic inundation.Flood-tolerant land uses (described below) will be much lessvulnerable to flood damages and therefore less likely to requiredisaster relief payments. Second, reconnection increases thearea available to store and convey floodwaters and can reduceflood risk for nearby areas. In most of the United States, thisbenefit occurs haphazardly through levee failure. For example,during 2008 floods in the U.S. Midwest, a town was spared becausea nearby levee protecting croplands failed, allowing floodwatersto inundate fields and alleviating pressure on the town’s levees(9). But strategic reconnection of floodplains, designed andimplemented to maximize public-safety benefits, holds greatpromise for reducing local and regional flood risk (8). Forexample, a study of the Illinois River found that reconnectionof 8000 hectares (ha) of floodplain would improve protectionfor 26,000 ha of farmland by halving the probability of inundationfrom major floods (10).

Large-scale reconnection of floodplains may also increase flexibilityand resilience of water-management infrastructure. Globally,thousands of large, multipurpose dams provide (or are beingbuilt to provide) flood control and water supply and/or hydropower.The need for partially empty reservoirs (to store floodwaters)must be balanced with the benefits from full reservoirs (watersupply, hydropower, recreation, and environmental flows to maintainhealthy ecosystems). Climate-change models suggest that manyregions of the world will experience increased frequency ofboth floods and droughts, exacerbating the challenge of balancingthese multiple objectives (1). Large-scale floodplain reconnectionprovides floodwater storage and conveyance, reducing the needfor upstream reservoirs to remain partially empty and thus increasingthe benefits they could provide when full. Increased resiliencyof water management systems through floodplain reconnectionis a promising example of ecosystem-based adaptation to climatechange.

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The author’s propose that there approach is demonstrated by the Yolo Bypass in California.

Demonstrating Success: The Yolo Bypass

Flooded Yolo Bypass

Although to date rarely implemented, this vision of large-scalefloodplain reconnection is not unprecedented. California’s YoloBypass conveys 80% of Sacramento River floodwaters during largeevents, routing water away from the city of Sacramento (seefigure, page 1487 ) (18). The bypass was created in the 1930sby reconnecting a 24,000-ha floodplain when it became apparentthat a “levees only” approach would not sufficiently reduceflood damages (19). By conveying large volumes of floodwaters,the bypass increases the flexibility of California’s water managementinfrastructure. During a March 1986 flood, the bypass conveyed12.5 billion cubic meters (bcm) of water, more than three timesthe total flood-control storage volume in all Sacramento basinreservoirs (3.5 bcm). This occurred during a period when theflood-control system was operating near maximum capacity (20).Without the bypass floodplain, California would need to buildmassive additional flood-control infrastructure or allocatemore of its already strained water-supply storage capacity toflood control.

Two-thirds of the bypass is privately owned, productive agriculture.During inundation, the bypass provides habitat for birds andnative fish (18). The bypass provides additional ecosystem services,such as open space for a rapidly growing region, recreation(including revenue-producing duck-hunting clubs), and groundwaterrecharge (of great value as a water bank during droughts) (14).